Which one of the following compounds is a peroxide?

Options

A. `KO_(2)`
B. `BaO_(2)`
C. `MnO_(2)`
D. `NO_(2)`

Answer

To determine which of the given compounds is a peroxide, we need to understand the definition and characteristics of peroxides. A peroxide contains the peroxide ion (O2^2-) where the two oxygen atoms are bonded together and carry a -2 charge overall.

Let's analyze each of the given compounds step by step:

1. **KO2 (Potassium Superoxide)**:
- Potassium (K) is an alkali metal with a fixed oxidation state of +1.
- The compound KO2 contains the superoxide ion (O2^-) instead of the peroxide ion. The oxidation state of the two oxygen atoms in KO2 is -1.
- Therefore, KO2 is not a peroxide.

**Hint**: Alkali metals like potassium have a fixed +1 oxidation state, leading to the formation of superoxide in KO2.

2. **BaO2 (Barium Peroxide)**:
- Barium (Ba) is an alkaline earth metal with a fixed oxidation state of +2.
- In BaO2, the two oxygen atoms are bonded together as the peroxide ion (O2^2-), which carries a -2 charge.
- The oxidation state of each oxygen in BaO2 is -1, confirming that it is indeed a peroxide.

**Hint**: Alkaline earth metals like barium have a +2 oxidation state, allowing the formation of the peroxide ion in BaO2.

3. **MnO2 (Manganese Dioxide)**:
- Manganese (Mn) is a transition metal and can have variable oxidation states.
- In MnO2, the oxidation state of Mn is +4 (since each oxygen has an oxidation state of -2).
- This compound does not contain the peroxide ion, so it is not a peroxide.

**Hint**: Transition metals can have multiple oxidation states, and MnO2 does not contain the peroxide ion.

4. **NO2 (Nitrogen Dioxide)**:
- Nitrogen (N) is a nonmetal and can also exhibit variable oxidation states.
- In NO2, nitrogen has an oxidation state of +4 (with each oxygen at -2).
- This compound does not contain the peroxide ion, so it is not a peroxide.

**Hint**: Nonmetals like nitrogen can also have variable oxidation states, and NO2 does not contain the peroxide ion.

**Conclusion**: The only compound that contains the peroxide ion (O2^2-) is **BaO2**.

**Final Answer**: BaO2 is the peroxide.

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